1. Field of the Invention
The present invention relates to an arrangement and method for Radio-Frequency (RF) high power generation comprising at least one power combiner having RF inputs and at least one RF output, and at least two power amplifier modules electrically connected to respectively an input by at least one transmission line, where at least one RF switch is formed by the at least one transmission line.
2. Description of the Related Art
Radio-Frequency (RF) and/or microwave power is produced with appropriate generators. RF power generators for high power applications are based on tubes, such as klystrons, inductive output tubes or magnetrons. Alternatively, solid state technology is used for RF power generators, particularly transistor technology. With solid state RF power generators, a reliable RF power production with small dimensions and high efficiency is possible. One disadvantage of transistor technology is a low RF power output per transistor chip, in the range of up to 1.5 kW power output at 500 MHz frequency. For comparison, with klystrons as an example for tube technology, up to a Megawatt level of RF power output is possible.
To generate high amounts of power with, for example, transistor based RF generators, an aggregation of RF generators is necessary. An aggregation of transistors in a single power amplifier PA based, for example, on push-pull or a balanced kind of topology, can increase the complexity of the system and increases the risk of failure. If single transistors fail, the entire device must be exchanged. An alternative way is to use a number of power amplifier modules with a common, particularly single power combiner. In a modular arrangement, RF power from the power amplifier modules, connected via transmission lines to the common power combiner, is aggregated in the power combiner to a high RF power level. For example, coaxial cables and/or strip-lines are used as transmission lines. The output power of power amplifier modules provided to the power combiner is adjusted and optimized to provide a high efficiency. A low reflection of power from inputs of the power combiner to the respective power amplifier module and low power transmission from a power amplifier module to other power amplifier modules, the “cross-talking” is ensured.
In case one or more power amplifier modules fails to operate, such as due to desired shutdown for stepped output RF power adjustment and/or due to defects/failure of power amplifier modules, such as due to overheating or transistor failure, the module does or modules do not generate RF power anymore, and at the respective power combiner input an arbitrary value of output impedance of the module is generated. The system is out of balance and crosstalk as well as mismatching, i.e., increased reflected RF power from the power combiner input, can as a result occur. A significant part of the total output RF power from still proper functioning power amplifier modules can be transferred through the power combiner to defect modules. These reduce the total RF power at an output-load that can be used by RF power consuming devices. The total efficiency of the power combiner system is reduced.
One possible conventional solution is the use of power combiners with a high amount of isolation between input ports, such as Wilkinson type power combiners. In case of failure of one or more power amplifier modules, a built in isolation resistor dissipates a significant amount of power from the remaining power amplifier modules. In this kind of power combiner, the cross-talking is reduced but the total power combining efficiency is also reduced, due to the output power dissipation in the isolation resistor.
Another possible conventional solution is to use circulators individually controlled at each output of an RF power amplifier module. In case of failure of a power amplifier module, reflected and cross-fed power will be dissipated in a dummy load connected to the respective circulator. The resultant total power efficiency of the power combining system is decreased because of a decrease of the available power at a load downstream to the power combiner.